Do You Need AIS On Your Boat?

When you are installing navigational equipment to your boat, you have almost certainly asked yourself whether you really need everything on the market. AIS, in particular, will be one of those. Lots of people rave about it, but is it really necessary to fit AIS on a small boat?

AIS is only compulsory on cargo ships over 300 GT; passengers ships; and most fishing vessels. Small, private boats generally do not need to have AIS fitted but may do so voluntarily to increase their own safety.

When do you need to have AIS on a boat?

On most small boats, it is not compulsory to carry AIS. The precise carriage requirements are defined within the International Convention for the Safety of Life at Sea (SOLAS). In there it states that AIS is compulsory on the following vessels:

“All ships of 300 gross tonnage and upwards on international voyages and cargo ships of 500 gross tonnage and upwards not engaged in international voyages and passenger ships irrespective of size…”


For other vessels, there are additional requirements to carry AIS in some areas. For example, within the European Union, the common fisheries policy means that most fishing vessels need to carry AIS, irrespective of the fact that they are below SOLAS carriage requirements. Read more about this particular example: EU Council Regulation 1224/2009

Similarly, the US Coast Guard require all fishing industry vessels to carry at least a Class B AIS transponder. You can read about their precise AIS requirements here: USCG AIS Requirements

For all the situations I have researched, small boats operated non-commercially do not need to have AIS fitted. Despite that, it is always best to contact your local authorities to check, just in case the laws in your region are different.

Assuming there is no legal obligation, it is entirely up to you to decide whether you need to carry AIS on your boat. In making your decision, there are a number of considerations you might want to take into account.

Why might you consider fitting AIS to your boat?

The biggest advantage of having AIS fitted on your boat is that it increases your chances of both seeing other vessels, and being seen yourself.

When you are using AIS, it acts as an extra pair of eyes helping you to keep a good lookout. In 2018, there was a collision between a powerboat and a ferry, where neither vessel saw the other. The powerboat was hidden in the glare from the sun, and the ferry came up from behind. 

Had AIS been fitted, it would have acted as a second lookout for the powerboat, alerting it to the presence of the ferry.

Similarly, from the point of view of other vessels, it acts as a beacon. It draws attention to your boat by placing you electronically on the screens of commercial vessels. In the same incident, had AIS been in use, the small powerboat would have shown up clearly on both the radar and the electronic chart of the ferry.

The incident in question was the collision between the ferry “Red Falcon” and the powerboat “Phoenix”. You can read the official accident report: Collision Between The Ro-Ro Passenger Ferry Red Falcon And The Motor Cruiser Phoenix

If you fit an AIS transponder to your boat, you will show up on all other vessels and stations that are using AIS. This includes all the vessels on which it is compulsory to carry AIS, as well as a growing number of pleasure boats that carry it voluntarily.

In addition to other vessels, you will appear automatically on monitoring equipment used by VTS or ports monitoring traffic in their area.

Pro Tip: Even if other vessels do not see you, VTS can monitor traffic so will attempt to alert other vessels to your presence if a collision looks likely.

Are there any other advantages to installing AIS?

As AIS is becoming more common on all sorts of vessels, it is starting to be used for more things than it was originally designed for.

Marine retailers now sell all sorts of devices that take advantage of AIS technology.

MOB devices

With AIS fitted on your own vessel, you can explore the use of AIS enabled man-overboard devices.

AIS man-overboard devices are designed to make it easier to locate a crew member that has fallen overboard. They are commonly used instead of a PLB because they can be detected by the crew member’s own vessel.

When a crew member falls into the water, the device activates and begins transmitting. The signal then shows up on the AIS display of your own vessel, as well as the displays of every other vessel in the area.

AIS man-overboard devices are particularly useful on vessels with multiple crew members, sailing in areas with little other traffic. You already have plenty of crew to help recover the person from the water. The MOB device just increases the likelihood of actually locating them.


AIS Search and Rescue Transponders (SARTs) are a more recent generation of the traditional radar SARTs.

While the traditional radar SART shows on up other vessel’s radars, the AIS SART shows up on the display of any vessel equipped with AIS. It can also show up on the display of coastal monitoring stations as well.

Both radar and AIS SARTs depend on other vessels having the necessary equipment for detecting them. If you have AIS fitted to your vessel, you would be able to detect AIS SARTs should you ever come across one.

While it is not a reason to fit AIS on your own vessel, it does illustrate how AIS technology is moving ahead and becoming more common throughout the industry.

Virtual ATONs

Virtual aids to navigation act in the same way as physical buoys and markers. Rather than providing a visual indication of an underwater hazard, they give an electronic indication.

They are not designed to replace the need for physical navigational aids, but it is becoming more common for them to be used in addition. The other huge advantage to virtual ATONs is that they can be rapidly deployed for new dangers to navigation.

A good example would be a recent shipwreck. It is very quick for the local harbour authority to establish a virtual marker while it could take a long time to establish physical buoyage.

To be able to “see” virtual ATONs, you need to be able to detect AIS signals. Fitting AIS to your vessel gives you the ability to locate these virtual markers. Integrating that with your electronic chart then visually places the new markers in their correct place, allowing you to navigate safely around them.

What are your options when considering AIS?

In deciding whether you need AIS, you have a few different options to choose between. There are full commercial units that are suitable for the world’s biggest ships; or there are smaller, lower power installations that are suitable for small boats.

Within those categories, you then need to decide whether you need the ability to transmit as well as receive, or whether you are happy to receive only.

Class A AIS

Class A AIS is suitable for merchant shipping and complies fully with the requirements of SOLAS. It is the most powerful type of AIS, having a typical power of 12W, and a correspondingly large transmission range.

The precise range of transmission is determined by the height of the antenna but typically ranges between 20-30 nautical miles.

Class A AIS takes the highest priority slots within the transmission block. If the geographical area is too busy, Class A AIS will be the last ones to drop. This means that AIS observations of larger vessels will remain more accurate than smaller vessels.

Generally, Class A AIS is significantly more expensive than Class B. As such, most smaller boats do not even consider fitting Class A, but it is still worth being aware of it when making your decision.

No matter what type of AIS you choose, you will always be able to detect transmissions from Class A vessels.

Class B AIS

Class B AIS is designed for use on vessels that fit AIS optionally. It is lower powered than Class A, having a typical power of 2W. Depending on the height of the antenna, you can expect a range of 5-6 nautical miles with Class B AIS.

As it cannot be used on compulsory vessels, Class B AIS is significantly cheaper than Class A. Add to that the lower power consumption due to the lower power transmissions, and you can see why it is used by recreational sailors.

It still transmits the same data, but the data has a lower priority. In a heavily congested area, Class B AIS will be the first ones to start dropping.

From a reception view, however, Class B AIS is no different from Class A AIS.

AIS Receivers

Should you decide that you want to fit Class B AIS, you then need to decide whether you want to transmit and receive, or just receive. If you do not want to transmit, you can fit an AIS receiver only.

AIS receivers give you a lot of the advantages of AIS. You can see other vessels, AIS beacons and virtual ATONs. You can even set automatic alarms so that you know when other AIS vessels are passing close to you.

The one disadvantage of a receiver, however, is that you will not show up on the AIS of other vessels. Going back to the arguments about “see and be seen”, an AIS receiver allows you to “see”, but won’t help you “be seen”.

AIS receivers are, however, much cheaper than transponders which transmit and receive. They bridge the gap between having no AIS and having full AIS.

AIS Transponders

AIS transponders are units that transmit as well as receive. If you need AIS on your vessel, a transponder will give you the full advantages of the AIS system.

Adding the ability to transmit gives you the ability to “be seen”. You will show up on the screens of vessels and other stations, like VTS operators.

As the price of the units comes down, more vessels are being fitted with Class B AIS transponders. While receivers let you see all those other vessels, a transponder will let them all see you too.

Using AIS with a chart plotter

The most common way to integrate a modern Class B AIS within a navigational system is to connect it to the chart plotter. While I wouldn’t actually say that AIS is needed with a chart plotter, it does add significantly to the chart plotter’s functionality.

Connecting AIS to the chart plotter lets you visualise the location and track of all the other vessels in your vicinity that are using AIS.

With current connectivity standards, it is surprisingly easy to accomplish as well. Assuming all your equipment uses NMEA 2000 standard, you simply plug in your AIS to the same network as your chart plotter. AIS data is then shared with everything on the network, including the plotter.

You may even have a wifi connection as well, which could then share AIS data with anything else you connect. Tablets, mobile phones or laptops are classic examples. Any of them could run a navigational app, and make full use of any AIS data you feed it.

Why you might not want AIS on your boat

While we have thoroughly discussed why you might need AIS on your boat, there are a couple of reasons that might mean you decide it isn’t needed.

AIS is expensive

Fitting a full transceiver can easily cost $1000, not to mention additional costs of setting it up. You can reduce the costs a lot if you decide to install a receiver alone, or if you combine the AIS with other equipment.

As AIS uses a VHF aerial, it makes sense to consider combining it with the VHF. VHF manufacturers do offer fixed sets now that include an AIS transponder. When you are due to replace the VHF, it is worth considering whether you want to use some of that investment towards a combined VHF/AIS instead.

Over-reliance of AIS

There have been countless reports of close calls or actual collisions as a result of relying too much on AIS data.

When equipment presents you with data is such a good way, it is easy to forget about its limitations.

As with everything, you should always remind yourself of the limitations of AIS, and take steps to account for those while using it. I have written a complete article on the limitations of AIS: What Are The Limitations Of AIS?

While I don’t think worrying about over-reliance is a reason to avoid AIS entirely, I do think it is important to be aware of the issue in general.

Not everyone else has it

In my view, the best argument for not fitting AIS is that there are lots of other boats that do not have it fitted.

You cannot see other boats on your system if they do not have it fitted.

While it will give you tremendous benefits when navigating in areas with commercial traffic, if you only ever navigate in areas with small boats then the benefits of AIS can be limited. 

In time, as more boats do fit AIS, it will become ever more beneficial to fit it yourself. For now though, you do need to assess whether it is worth the cost, especially if it is unlikely you will ever see another boat with it fitted.

My personal recommendation of AIS on small boats

I see the benefits of AIS from two different perspectives. My recommendation of whether AIS is needed on a boat changes depending on the perspective.

Firstly, as an officer navigating large ships, I would recommend every boat fits an AIS transponder. I’ve see situations at sea where the AIS signal drew attention to a small boat many miles before visual contact was possible. 

Most small boats are made of fiberglass, making radar contact difficult. AIS removes all those difficulties, just increasing the visibility of every vessel carrying it.

Secondly, as a small boat sailor, I would say to fit AIS if you can afford to do so. Boats are often expensive, so most people that can afford one should be able to fit AIS. Fitting a transponder combined with a VHF, can be a very affordable way of getting AIS.

It isn’t essential, but it is a piece of equipment that can instantly increase the safety of both you and your boat.